This invention relates in general to air compressors and in particular to air compressor apparata including noise-reducing means.
Air compressor apparata and related equipment are currently manufactured in a wide range of styles and capacities. Air compressors may be either oil-less or lubricated and operate on the theory of intaking ambient air and transforming this ambient air into compressed air which may then either be stored in a reservoir tank or delivered directly to a remote use location. Compressed air has a variety of uses such as for operating small hand tools and for medical and dental equipment. Air compressors may be either a rotary-vane style or a piston style and the requirements of the related equipment with which the air compressor is used govern what horsepower size unit is most appropriate.
In certain applications, it is quite important that the supplied compressed air be oil-free as well as dry. Consequently, an oil-less air compressor must be selected and coupled to a refrigerant dryer or similar device in order to remove a majority of the moisture which is commonly found within ambient air. Although the variety of compressors seems somewhat endless, all compressors are alike in that their operation generates a noticeable amount of heat as well as noise. While many compressors incorporate blowers and finned heat sinks to reduce the effect of the elevated temperatures generated, very little has been done to combat the level of noise which is also generated. While noise is not directly harmful in most situations, it is quite undesirable in virtually every medical and dental application due to its distracting and annoying aspects.
In an effort to try and muffle or reduce noise, a variety of compressor enclosures have been conceived. The following five patent references disclose certain ones of these enclosure concepts:
______________________________________ Patent No. Patentee Issue Date ______________________________________ 2,928,589 Davey 3/15/60 3,698,840 Hover 10/17/72 3,905,204 Edwards 9/16/75 2,721,028 Dills 10/18/55 3,612,213 Piko 10/12/71 ______________________________________
Davey discloses a hermetically sealed motor compressor unit including noise-reducing means. The noise of concern is the result of vibrations and is collectively referred to as "cavity resonance." This noise is decreased by providing between the outer casing and the compressor unit a curtain of woven cloth.
Hover discloses a compressor muffler construction for a gas pump which has an improved dampening capability for pressure pulses induced by the pump to provide a reduced noise level with less flow restriction losses.
Edwards discloses an auxiliary porting arrangement for noise control of an air-conditioning compressor-expander. The compressor inlet port and expander outlet port are so positioned that the volume of an exiting charge of air is less than the volume of an entering charge of air in a predetermined ratio so that air is discharged at nominally ambient pressure.
Dills discloses an arrangement for reducing the case resonance of a high-speed compressor to a lower level where it is not objectionable and for reducing the driven noise that comes through the compressor casing. The arrangement includes a series of shock absorbers disposed adjacent the exterior of the compressor casing and held in position by a strap.
Piko discloses a silent housing for air pumps and compressors which is fabricated of sound-deadening material and includes a pair of air intake resonant valves tunable to an upper frequency of the pump or compressor. The housing further includes a pair of outlet valves tuned to the same frequency as the intake valves.
Although the disclosed concepts of these various patent references may have provided some innovation at the time of their conception, each of these devices have the same two disadvantages. First, the primary manner of noise reduction is by reducing vibration and case resonance and nothing is done to dampen or reduce the internal noise generated by the operation of the compressor. Secondly, with each arrangement which encloses the compressor, sufficient cooling means are not provided in order to reduce the heat buildup within the enclosure and thus enable the compressor to continue to operate within a safe ambient temperature range. Although enclosing the compressor may reduce noise, it also traps all generated heat which quickly creates an interior temperature which can adversely affect the compressor and its operation. Thus, it would be an improvement to such compressor arrangements to provide a soundproofing enclosure with a suitable air circulation construction to enable noise reduction as well as maintenance of a safe interior temperature.